Annealing, hardening and heat treatment of carbon tool steel.
Heat treatment pretreatment
The peculiarity of all grades of unalloyed tool steels is their non-cross hardenability along the tool section. This explains their application at small operational loads and for production of relatively small cross-section items, e.g. cutters, dies, punches, etc. Before the hardening the steel is annealed, this is an operation that improves mechanical properties of material along the section and evens out the chemical composition. The subsequent machinability is also improved and permanent deformations are reduced.
Types of annealing
- Recrystallization annealing, after which the overlap is removed. The mode of execution is temperature of 670...700°С, holding with the furnace up to one hour;
- Full, the purpose of which is to reduce the hardness to correct the detected defects of the structure. Mode: heating in the furnace to 800 ... 860 ° C until the complete heating of the section of the workpiece. This is followed by slow cooling to 500 ... 600 ° C, after which the cooling rate of products can be any;
- Theincomplete annealing is conducted by the same technology as the complete one, but the temperature of heating must be 70 ... 100°C lower. The incomplete annealing is carried out after the ingots are forged;
- Isothermal, the purpose of which is to provide a favorable microstructure of the tool carbon steel before hardening. The mode is heating to 750 ... 800 ° C and holding at 600 ... 650 ° C to obtain the hardness level of 170 ... 207 NV.
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Hardening
Hardening modes of tool carbon steels are selected taking into account the following factors:
- Ensuring the required cross-sectional hardenability - high surface hardness with an optimally ductile core;
- Obtaining the structure of either martensite with residual austenite, or ferrite-carbide mixture (sorbitol and troostite quenching);
- The technological purpose of the part;
- Reduction of stresses and strains in the parts after quenching, which increases the dimensional accuracy of heat-treated products.
Critical diameter
Critical diameter of the tool, mm, made of carbon tool steels, at hardening in various environments is given in the table.
| Steel grade | Hardening medium | |||
| Water | Oil | Saltpetre | Air | |
| U7, U7A | 15...20 | 4...6 | 4...6 | Not quenched |
| У8, У8А | 15...20 | 4...6 | 4...6 | Not hardened |
| У10, У10А | 15...20 | 4...6 | 4...6 | Not hardened |
| У11, У11А | 15...20 | 4...6 | 4...6 | Not hardened |
| У12, У12А | 10...12 | 4...6 | 4...6 | Not hardened |
| У13, У13А | 10...12 | 4...6 | 4...6 | Not hardened |
To buy. Supplier, price.
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